Standard and Technology of Full-Dimension MINO Systems in LTE-Advances Pro Massive MIMO has been studied in academia foreseeing the capacity crunch in the coming years. Presently, industry has also started to pay attention to realizing the initial stage of massive MIMO system. A few proof-ofconcept systems are being reported recently. In addition, 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) has finished a Study Item (SI) on Full-Dimension MIMO (FD-MIMO). The SI investigated feasibility of FD-MIMO systems which support up to 64 transceiver units (TXRUs) with 2D antenna arrays that have a similar form factor as existing base station antennas. The scope of the SI involves both Time-Division- Duplex (TDD) and Frequency-Division Duplex (FDD), so that the technology can be used in the existing 4G cellular carrier frequency. This article provides an overview of challenges and corresponding design considerations for standardizing FD-MIMO, including the outcomes of the SI. In particular, potential enhancements in Channel State Information (CSI) feedback design will be investigated in details. Keywords: FD-MIMO, 3D beamforming, 2D array antenna
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